1. Field of the Invention
The present invention relates to a package structure of a controller module for power conversion applications, especially to a package structure of a controller module including a start-up component, a controller, and a power switch.
2. Description of the Related Art
Please refer to FIG. 1a, which illustrates a circuit diagram of a prior art power converter, and FIG. 1b, which illustrates the package structure of a controller module applicable in the prior art power converter of FIG. 1a. As illustrated in FIG. 1a, the prior art power converter includes a PWM (pulse width modulation) controller 100, a first NMOS (n type metal oxide semiconductor) transistor 110, a second NMOS transistor 120, a primary coil 130 for transferring power to a load, and an auxiliary coil 140 for generating a supply voltage VCC; and in FIG. 1b, the controller module is in the form of an integrated circuit package having a package structure integrating a chip 100c of the PWM controller 100, a chip 110c of the first NMOS transistor 110, and a chip 120c of the second NMOS transistor 120 of FIG. 1a. 
The PWM controller 100 has two contacts for connecting with the first NMOS transistor 110, one contact for connecting with the supply voltage VCC, and one contact for providing a PWM signal VPWM to switch on/off the second NMOS transistor 120 for realizing a power conversion.
The first NMOS transistor 110, having a first drain coupled to a first end A of the primary coil 130, a first gate connected to one contact of the PWM controller 100, and a first source connected to another contact of the PWM controller 100, is used as a start-up component, which is switched on to provide a current path for starting up the PWM controller 100 during an initial period after an AC power VAC is applied, and is switched off by the PWM controller 100 when the supply voltage VCC is built up. That is, when the supply voltage VCC reaches a predetermined level, the PWM controller 100 will send a low voltage to the first gate of the first NMOS transistor 110 to switch off the first NMOS transistor 110.
The second NMOS transistor 120, acting as a power switch, has a second drain coupled to a second end B of the primary coil 130, a second gate coupled with the PWM signal VPWM, and a second source connected with a current sensing resistor for generating a current sensing signal VCS according to a primary current IP. The second NMOS transistor 120 controls an on period for the primary current IP to flow through the primary coil 130 in response to the PWM signal VPWM.
The package structure in FIG. 1b includes the chip 100c of the PWM controller 100, the chip 110c of the first NMOS transistor 110, the chip 120c of the second NMOS transistor 120, a resin material 200, a first die pad 210, a second die pad 220, a third die pad 230, and eight external connection leads.
The resin material 200 is used to enclose the chip 100c of the PWM controller 100, the chip 110c of the first NMOS transistor 110, the chip 120c of the second NMOS transistor 120, the first die pad 210, the second die pad 220, and the third die pad 230.
The first die pad 210 is made of a conductor, copper for example, for carrying the chip 110c of the first NMOS transistor 110. The chip 110c of the first NMOS transistor 110 has a top surface providing a gate contact G1 and a source contact S1, and a bottom surface providing a drain contact D1 which is electrically connected with the first die pad 210.
The second die pad 220 is made of a conductor, copper for example, for carrying the chip 100c of the PWM controller 100.
The third die pad 230 is made of a conductor, copper for example, for carrying the chip 120c of the second NMOS transistor 120. The chip 120c of the second NMOS transistor 120 has a top surface providing a gate contact G2 and a source contact S2, and a bottom surface providing a drain contact D2 which is electrically connected with the third die pad 230.
The interconnections among the chip 100c, the chip 110c, the chip 120c, and the external connection leads are accomplished by wires, which can be made of copper, gold, or aluminum. As can be seen in FIG. 1b, a wire 251 connects the first die pad 210 with an external connection lead 241 of the eight external connection leads, and a wire 252 connects the third die pad 230 with an external connection lead 242 of the eight external connection leads, wherein the external connection lead 241 is used to connect electrically with the first end A of the primary coil 130, and the external connection lead 242 is used to connect electrically with the second end B of the primary coil 130.
As the die pads constitute a substantial portion of the cost of the package structure of the controller module, it is therefore desirable to reduce the number of die pads to promote the market competition ability of the controller module. However, as can be seen in FIG. 1a and FIG. 1b, the first die pad 210, the second die pad 220, and the third die pad 230 all seem to be necessary for implementing the controller module. For example, if we put the chip 110c and the chip 120c into one die pad to save one die pad, then the drain contact D1 will be in direct electrical contact with the drain contact D2, making the power module not applicable for the prior art power converter of FIG. 1a. Therefore, it is not easy to reduce the cost of the package structure of the controller module for power converters.